CAPjoint , A Computer Software Package for Joint Inversion of Moderate Earthquake Source Parameters with Local and

Accurate earthquake source parameters such as fault mechanism, depth, and moment magnitude are not only important in seismic-hazard assessment, but also are crucial to studies of earthquake rupture processes and seismotectonics. Although large earthquakes (Mw 7+) may cause substantial damage, they occur less frequently. In contrast, moderate earthquakes (Mw 5.0–6.5) occur with much higher frequency and may occur on faults not geologically identified. Some of the moderate earthquakes cause damage in densely populated communities, especially in developing countries (Baumbach et al., 1994; Hamzehloo, 2005). For example, the 2011 Mw 5 earthquake in Lorca, Spain (Pro et al., 2014), the 2012Mw 5.9 Ferrara earthquake sequence in northern Italy (Malagnini et al., 2012), the 2010Mw 5 Suining earthquake in Sichuang Province of China (Luo et al., 2011), and the 1998 Mw 5.7 Zhangbei earthquake in Hebei Province of China (Li et al., 2008) all caused substantial economic loss and casualty. Compared with events larger than Mw 7, rupture processes of these moderate events can be approximated as point sources, which are usually described with a centroid moment tensor (CMT) because the rupture duration is usually shorter than the period used in the waveform inversion. Many algorithms and software packages have been developed to invert CMT parameters using seismic waveform data. For example, long-period teleseismic waveforms have been routinely used to determine source parameters, such as a W phase solution, Global CMT catalog, and U.S. Geological Survey (USGS) fast moment tensor solutions (Dziewonski et al., 1981; Ekström et al., 2012). However, centroid depth is usually not well resolved in these long-period solutions. Centroid depth estimation is improved with teleseismic body-wave solutions (Chen and Molnar, 1983; Saikia, 2006), which are also routinely reported by National Earthquake Information Center (NEIC)/USGS for Mw 6+ earthquakes. With a bootstrapping approach, Zhan et al. (2012) confirm that centroid depth and dip angle can be accurately resolved with inversion of teleseismic body-wave data when the earthquakes are recorded at many seismic stations (Zhan et al., 2012). When moderate earthquake records are not clipped, local seismic waveform data can be used in modeling source parameters of moderate earthquakes; examples are the routine moment tensor solutions by Northern California Earthquake Center and Saint Louis University (Dreger and Helmberger, 1993; Dreger et al., 2000; Herrmann et al., 2011). To avoid the overweighting problem of surface wave in full-waveform inversion, a method called cut and paste (CAP) was developed, in which seismic waveforms are separated into body waves and surfaces waves (Zhao and Helmberger, 1994; Zhu and Helmberger, 1996). Several software packages were introduced based on all these different waveform inversion algorithms (Zwick et al., 1994; Ichinose et al., 1997; Saikia, 2006; Sokos and Zahradnik, 2008). Mw 5.5+ earthquakes are usually well recorded at both teleseismic and local distances. Intuitively, a combination of both teleseismic and local seismic waveforms provides more constraints on earthquake source parameters. Using inversion of local waveform data and forward modeling of teleseismic body waveforms, Wei et al. (2009) confirmed that an Mw 5.8 earthquake in northern China occurred in the lower crust. Chen et al. (2012) developed a method of joint inversion with teleseismic and local seismic waveforms; they found that joint inversion improves either accuracy of centroid depth as compared with local waveform inversion only or accuracy of fault-plane parameters as compared with teleseismic waveform inversion only (Chen et al., 2012). The necessity for joint inversion of teleseismic and local waveforms is more obvious for studies of recentMw 5 events recorded by sparse networks and particularly earthquakes decades ago. For example, in the early 1990s, seismic network coverage was sparse, and a moderate earthquake was well recorded with only a few teleseismic and local stations. Inversion of only teleseismic or local seismic waveform data does not have enough data for good constraints on source parameters. Even for Mw 5 earthquakes occurring in the present day, joint inversion is still necessary because seismic networks are very sparse in most regions of the world (except California, Japan, etc.) and earthquakes in these regions are usually recorded with only one or two stations. At the same time, only a few seismic stations are available with clear teleseismic body wave for inversion. In this article, we presented a software package for source parameter inversion (moment magnitude, fault-plane parameters, and centroid depth) of moderate earthquakes, with local or teleseismic waveforms independently or for joint inversion with both datasets (the software package and the user’s manual